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Key outcomes

  • Mitigated risk
  • Reduced emissions and operating costs
  • Provided never-before-seen understanding of the internal behaviour

Synergetics used CFD modeling to predict the temperature of combustion by-products in a biosolids multiple hearth furnace (MHF). The CFD modeling included the drying and devolatilization processes, as well as combustion. MHFs are used worldwide for various applications such as calcination, carbon activation/regeneration, and biosolids incineration.


The top levels of an MHF showing the drying and combusting biosolids and the hot gases generated by the combustion.

Figure 1: Hot combustion gasses created by hearth two combustion.

Validating the model was critical to providing reliable predictions since performing CFD simulations of a MHF was a novel approach. Synergetics validated the model by conducting an onsite data measurement campaign. This campaign included temperature and gas sensor readings at the furnace exit and stack, as well as with lab tests on biosolids feed composition. These measurements provided accurate inputs for the model and outputs for validation.

Our client set a target difference of 20% for hearth temperatures and exit gas O2, CO and CO2 levels to consider the model valid. We performed validation under two sets of operating conditions. Strong agreement was observed, with all validated quantities well under the 20% criteria.

The next stage was to use the model to predict the impact of future operational loads on the furnace and identify potential issues. Based on the model’s output, Synergetics provided design and operational recommendations aimed at reducing emissions and operating costs. They also simulated and assessed a range of proposed engineering changes to find the optimal solution. This approach mitigated the client’s risk of making costly capital changes without achieving the desired improvements in stability and emissions.

Figure 2: An animation demonstrating the rabble arms raking the cake and showing its motion.


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